Accuracy and precision of age determination techniques for Mississippi River bighead carp Hypophthalmichthys nobilis (Richardson 1845) using pectoral spines and scales

Age determination techniques for bighead carp Hypophthalmichthys nobilis from the Mississippi River (MR) were investigated. Sagittal otoliths, cleithrum bones, scales, and pectoral spines were obtained from bighead carp collected from the middle Mississippi River (MMR) and from Pool 26 of the MR. Known-age bighead carp (Age 1, N = 3 and age 2, N = 5) pond-reared in a fish farm were used to aid in the interpretation and validation of age assessments. Sagittae and cleithra were cloudy and annuli were difficult to identify both in whole view and sectioned; they were not evaluated further. All pectoral spine sections (N = 98) and scales (N = 57) from known-age and unknown-age specimens were read by three readers. Readers were provided with the date of capture and were not informed of the presence of known-age bighead carp. Percent agreement among age estimates from unknown-age bighead carp was 19% for scales and 23% for spine sections. There was approximately 60% agreement within one year for both structures. Agreement for age 1 bighead carp using scales was 100%, and 20% for age 2 specimens. Using spine sections, agreement was 67% for both age 1 and age 2 known-age bighead carp. Mean percent accuracy interpreting the age of known-age bighead carp was 69% for spine sections and 78% for scales. Accuracy of scale readings was 100% for age 1 and 60% for age 2. A multiple regression analysis of age estimates by the readers showed no significant difference (p > 0.05) between the aging structures and the dependent variable, estimated age, but a significant aging structure by mean estimated age interaction was found. Scales yielded lower age estimates than spine sections for older bighead carp, while spine sections yielded lower age estimates for younger bighead carp. We suggest using pectoral spine sections to age older bighead carp (2 and older), because they showed more and sharper annuli than scales.